Thiomethylphenols are widely used as an important antioxidant in plastics, elastomers, mineral oils and synthetic oils.
With regard to a process for manufacturing the thiomethylphenol derivatives, U.S. Pat. No. 4,091,037 discloses a process comprising the step of reacting 2-(dimethylaminomethyl)-4-methylphenol with thioacetic acid. U.S. Pat. No. 4,304,940 discloses a process comprising the step of reacting phenol with paraformaldehyde and mercaptan derivatives in the presence of Zn(OAc)2. Korean patent publication No. 1995-9748 and U.S. Pat. No. 4,874,885 disclose a process for preparing a yellow liquid of thiomethylphenol derivatives, which comprises the step of reacting formaldehyde and mercaptan derivative in a solvent such as N,N-dimethylformamide at 155° C. for 2 hours in the presence of a base such as mono-, di-, or trimethylamine or mono- or diethylamine.
Besides, Korean patent application No. 2001-0000988 and U.S. Pat. No. 6,365,781 disclose a process for preparing thiomethylphenol derivatives, which comprises the step of reacting formaldehyde and mercaptan derivatives in the presence of mono, di, or trimethylamine or mono or diethylamine base without using a solvent at 130° C. for 3.5 hours, and treating the products with a reducing agent at 90° C. for 7 hours. In theses patents, the base is limited to mono dimethylamine, dimethylamine, monoethylamine and diethylamine.
However, the aforementioned processes have drawbacks that they require a high reaction temperature, a long period of time for either the reaction or the purification, and a discoloration resulted from the oxidation of a base.
Therefore, an object of the present invention is to provide a process for preparing colorless thiomethylphenol derivatives, which may increase the reaction rate and improve discoloration even at a relatively mild condition.